User equipment and access node and respective methods

ABSTRACT

A user equipment (UE) for which an analog beamforming scheme is applied and a measuring method performed by the UE are provided. Also an access node (AN) and a method performed by the AN are provided. The measuring method performed by the UE comprising: transmitting, to a serving access node, a measurement request for measuring a neighbouring access node that is working at a same frequency as the user equipment; receiving, from the serving access node, information related to a series of measurement time gaps; and after a delay, performing a measurement to the neighbouring access node within the series of measurement time gaps.

TECHNICAL FIELD

The present disclosure relates to measurement in a wireless network andin particular to measurement in a MMW (Millimeter Wave)-based wirelessnetwork.

BACKGROUND

Ultra Dense Networks, UDNs are generally regarded as the next generationcommunication system following the 3rd Generation Partnership ProjectLong Term Evolution (3GPP LTE) system. They are expected to provide datarates up to 10 Gbit/s and even higher, which might meet userrequirements for increasing data traffic.

MMW is one of candidate techniques for the next generation communicationsystem (i.e. UDN) due to its high frequencies and huge license-freebandwidth at these frequencies. Compared with technologies operating atlower frequencies, however, MMW may suffer more severe signalattenuation and higher total noise power which result in very shorttransmission distances. In order to solve this problem, an antenna-arraybeamforming technology is used which is a promising technology and canenhance intensity of signals or increase transmission distancessignificantly.

There are two main schemes about the antenna-array beamformingtechnology. One is a digital beamforming scheme, and the other is ananalog beamforming scheme. With respect to both of the two beamformingschemes, weighting operations are generally performed to signals whichare to be transmitted from an antenna-array of Access Node (AN) andreceived by antennas of an antenna-array of a UE (User Equipment), orvice versa. Different weighting operations form different beamformingpatterns which thus result in different effects. The digital beamformingscheme performs weighting operations to signals in digital domain andcan thus achieve an effect which looks like that signals from alldirection can be received simultaneously by an antenna-array of a UE.However, the analog beamforming scheme performs weighting operations tosignals in analog domain and can thus achieve an effect which looks likethat signals from only one direction can be received at a certain timeby the antenna-array of the UE.

In the digital beamforming scheme, since the weighting operation is donein digital domain, each antenna branch needs a dedicatedAnalog-to-Digital Converters (ADC). But in the analog beamformingscheme, since the weighting operation is implemented in analog domainbefore a common ADC, an antenna-specific ADC can be avoided. Sincecomplexity and cost of the analog beamforming scheme are lower than thedigital beamforming scheme, the analog beamforming scheme is preferablyused for UEs or ANs in a MMW-based network. In the current 3GPP LTEnetwork, however, the digital beamforming scheme is used for UEs or ANs.Since, as described above, the effect achieved by the digitalbeamforming scheme is different from that achieved by the analogbeamforming scheme, mechanisms for UEs or ANs using the digitalbeamforming scheme may not work for UEs or ANs using the analogbeamforming scheme.

One of the mechanisms is intra-frequency measurement performed duringcell search. In the 3GPP LTE network, intra-frequency measurement refersto a situation in which a neighbouring AN which is working at the samefrequency as a served UE being currently serviced by a serving AN, isdetected by the served UE. Since the neighbouring AN, the serving AN andthe UE work at the same frequency and the digital beamforming scheme isused by the UE, the UE can receive, in terms of actual effect, a signalfrom the neighbouring AN while performing data communication with theserving AN at the same time. Therefore, in the 3GPP LTE network,measurement to the neighbouring AN and data communication with theserving AN are arranged to be performed simultaneously.

With respect to UEs using the analog beamforming scheme, however, theabove mechanism can not work since the UEs can receive, in terms ofactual effect, signals in only one direction at a certain time. When aserved UE is performing data communication with a serving AN,measurement to a neighbouring AN which is working at the same frequencyas the served UE can not be performed by the served UE. Therefore, ifthe cell searching mechanism of the 3GPP LTE network is directly used ina MMW-based network, those neighbouring ANs which are working at thesame frequency as the served UE can not be detected.

Generally speaking, a system signal, such as a reference signal or asynchronization signal should be periodically transmitted by an AN toits served UEs, so that the served UEs can know information about theAN. Furthermore, in UDN networks, it is more possible for ANs to uselonger system signal period in order to save power consumption.Therefore, a UE will take much more time to capture a system signal of aneighbouring AN if it starts measurement to the neighbouring ANrandomly.

SUMMARY

The object is to obviate at least some of the problems outlined above.In particular, it is an object to provide a UE for which an analogbeamforming scheme is applied and a measuring method performed by theUE. It is further an object to provide an AN and a method performed bythe AN. These objects and others may be obtained by providing a UE andan AN respectively and a respective method performed by the UE and theAN according to the independent claims attached below.

According to an aspect there is provided a measuring method performed bya user equipment for which an analog beamforming scheme is applied. Themethod comprises transmitting, to a serving access node, a measurementrequest for measuring a neighbouring access node which is working at thesame frequency as the user equipment; receiving from the serving accessnode, information related to a series of measurement time gaps; andafter a delay, performing measurement to the neighbouring access nodewithin the series of measurement time gaps.

Within each of the series of measurement time gaps, the performing stepcomprises suspending data communication with the serving access node;adjusting a beamforming pattern of the user equipment; and detecting asystem signal of the neighbouring access node.

The method further comprises after the detecting step, re-adjusting thebeamforming pattern of the user equipment; and restoring the datacommunication with the serving access node.

The information comprises length of the delay, a period of the series ofmeasurement time gaps, and length of each measurement time gap.

The period of the series of measurement time gaps is a multiple of aperiod of a system signal of the neighbouring access node, and thelength of each measurement time gap is equal to a sum of an offset andlength of a transmitting time gap within which the system signal of theneighbouring access node is transmitted.

The method further comprises after the receiving step, after anotherdelay, performing measurement to another neighbouring access node withinanother series of measurement time gaps, wherein the anotherneighbouring access node is working at the same frequency as the userequipment, and information related to the another series of measurementtime gaps is included in the information related to the series ofmeasurement time gaps.

The delay is different from the another delay and the series ofmeasurement time gaps do not overlap the another series of measurementtime gaps.

According to yet an aspect a method performed by an access node isprovided. The method comprises determining information related to aseries of measurement time gaps in response to receiving from a serveduser equipment a measurement request for measuring a neighbouring accessnode which is working at the same frequency as the user equipment;transmitting the information to the served user equipment.

The method further comprises after the transmitting step, suspendingdata communication with the served user equipment.

The method further comprises before the determining step, obtaining thesystem signal of the neighbouring access node from the neighbouringaccess node, wherein the information is determined at least based on thesystem signal of the neighbouring access node.

The information comprises: a delay, a period of the series ofmeasurement time gaps, length of each measurement time gap.

The method further comprises determining information related to anotherseries of measurement time gaps in response to receiving from the serveduser equipment a measurement request for measuring another neighbouringaccess node which is working at the same frequency as the userequipment, and the information related to the another series ofmeasurement time gaps is included in the information related to theseries of measurement time gaps.

The series of measurement time gaps do not overlap the another series ofmeasurement time gaps.

If a transmitting time gap of the system signal of the neighbouringaccess node does not overlap that of the system signal of the anotherneighbouring access node, a delay corresponding to the neighbouringaccess node is different from that corresponding to the anotherneighbouring access node, and a period of the series of measurement timegaps is a multiple of a period of the system signal of the neighbouringaccess node and a period of the another series of measurement time gapsis a multiple of a period of the system signal of the anotherneighbouring access node.

If a transmitting time gap of the system signal of the neighbouringaccess node overlaps that of the system signal of the anotherneighbouring access node, a delay corresponding to the neighbouringaccess node is different from that corresponding to the anotherneighbouring access node, and a period of the series of measurement timegaps is at least twice as long as a period of the system signal of theneighbouring access node, and a period of the another series ofmeasurement time gaps is at least twice as long as a period of thesystem signal of the another neighbouring access node.

According to still an aspect a user equipment is provided for which ananalog beamforming scheme is applied. The user equipment is adapted totransmit, to a serving access node, a measurement request for measuringa neighbouring access node which is working at the same frequency as theuser equipment; receive, from the serving access node, informationrelated to a series of measurement time gaps; and after a delay, performmeasurement to the neighbouring access node within the series ofmeasurement time gaps.

Within each of the series of measurement time gaps, the performing stepcomprises suspending data communication with the serving access node;adjusting a beamforming pattern of the user equipment; detecting asystem signal of the neighbouring access node.

The user equipment is further adapted to re-adjust the beamformingpattern of the user equipment; and restore the data communication withthe serving access node.

The user equipment is further adapted to after the receiving step, afteranother delay, perform measurement to another neighbouring access nodewithin another series of measurement time gaps, wherein the anotherneighbouring access node is working at the same frequency as the userequipment, and information related to the another series of measurementtime gaps is included in the information related to the series ofmeasurement time gaps.

According to another aspect an access node is provided. The access nodeis adapted to determine information related to a series of measurementtime gaps in response to receiving from a served user equipment ameasurement request for measuring a neighbouring access node which isworking at the same frequency as the user equipment; and transmit theinformation to the served user equipment.

The access node is further adapted to after the transmitting step,suspend data communication with the served user equipment.

The access node is further adapted to before the determining step,obtain the system signal of the neighbouring access node from theneighbouring access node, wherein the information is determined based onthe system signals of the neighbouring access node.

The information comprises a delay, a period of the series of measurementtime gaps, length of each measurement time gap.

The access node is further adapted to determine information related toanother series of measurement time gaps in response to receiving fromthe served user equipment a measurement request for measuring anotherneighbouring access node which is working at the same frequency as theuser equipment; and transmit, to the served user equipment, theinformation related to the another series of measurement time gaps.

According to yet an aspect a user equipment is provided for which ananalog beamforming scheme is applied. The user equipment comprises aprocessor and a memory. The memory comprises instructions which whenexecuted by the processor causes the user equipment to transmit, to aserving access node, a measurement request for measuring a neighbouringaccess node which is working at the same frequency as the userequipment; receive, from the serving access node, information related toa series of measurement time gaps; and after a delay, performmeasurement to the neighbouring access node within the series ofmeasurement time gaps.

Within each of the series of measurement time gaps, the performing stepcomprises: suspending data communication with the serving access node;adjusting a beamforming pattern of the user equipment; and detecting asystem signal of the neighbouring access node.

The memory further comprises instructions, which when executed by theprocessor causes the user equipment to re-adjust the beamforming patternof the user equipment; and restore the data communication with theserving access node.

The memory further comprises instructions, which when executed by theprocessor causes the user equipment to after the receiving step, afteranother delay, perform measurement to another neighbouring access nodewithin another series of measurement time gaps, wherein the anotherneighbouring access node is working at the same frequency as the userequipment, and information related to the another series of measurementtime gaps is included in the information related to the series ofmeasurement time gaps.

According to still an aspect an access node is provided. The access nodecomprises a processor and a memory. The memory comprises instructionswhich when executed by the processor causes the access node to determineinformation related to a series of measurement time gaps in response toreceiving from a served user equipment a measurement request formeasuring a neighbouring access node which is working at the samefrequency as the user equipment; and transmit the information to theserved user equipment.

The memory further comprises instructions, which when executed by theprocessor causes the access node to after the transmitting step, suspenddata communication with the served user equipment.

The memory further comprises instructions, which when executed by theprocessor causes the access node to before the determining step, obtainthe system signal of the neighbouring access node from the neighbouringaccess node, wherein the information is determined at least based on thesystem signal of the neighbouring access node.

The information comprises a delay, a period of the series of measurementtime gaps, length of each measurement time gap.

The memory further comprises instructions, which when executed by theprocessor causes the access node to determine information related toanother series of measurement time gaps in response to receiving fromthe served user equipment a measurement request for measuring anotherneighbouring access node which is working at the same frequency as theuser equipment; and transmit, to the served user equipment, theinformation related to the another series of measurement time gaps.

According to still an aspect a user equipment is provided for which ananalog beamforming scheme is applied. The user equipment comprises atransmitting unit for transmitting, to a serving access node, ameasurement request for measuring a neighbouring access node which isworking at the same frequency as the user equipment; a receiving unitfor receiving, from the serving access node, information related to aseries of measurement time gaps; and a performing unit for after adelay, performing measurement to the neighbouring access node within theseries of measurement time gaps.

According to another aspect an access node is provided. The access nodecomprises a determining unit for determining information related to aseries of measurement time gaps in response to receiving from a serveduser equipment a measurement request for measuring a neighbouring accessnode which is working at the same frequency as the user equipment; and atransmitting unit for transmitting the information to the served userequipment.

According to yet an aspect a computer program is provided. The computerprogram comprises instructions which, when executed on at least oneprocessor, cause the at least one processor to carry out the methodaccording to the method performed by the UE.

According to still an aspect a computer program is provided. Thecomputer program comprises instructions which, when executed on at leastone processor, cause the at least one processor to carry out the methodaccording to the method performed by the AN.

The method performed by a UE and the method performed by an AN as wellas the UE and the AN may have several advantages. In a wireless network,especially a MMW-based network, through the AN providing informationabout measurement time gap to the UE, the UE may take a little time toperform measurement, thus increasing time efficiency and decreasingpower consumption. Furthermore, through suspending data communicationbetween the UE and the AN during measurement, data lost can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will now be described in more detail in relation to theaccompanying drawings, in which:

FIG. 1 is a flowchart of a measuring method performed by a UE for whichan analog beamforming scheme is applied according to an exemplifyingembodiment.

FIG. 2 is a flowchart of a method performed by an AN according to anexemplifying embodiment.

FIG. 3 is a block diagram of a UE for which an analog beamforming schemeis applied according to an exemplifying embodiment.

FIG. 4 is a block diagram of an AN according to an exemplifyingembodiment.

FIG. 5 is a block diagram of a UE for which an analog beamforming schemeis applied according to an exemplifying embodiment.

FIG. 6 is a block diagram of an AN according to an exemplifyingembodiment.

FIG. 7 is a block diagram of a UE for which an analog beamforming schemeis applied according to an exemplifying embodiment.

FIG. 8 is a block diagram of an AN according to an exemplifyingembodiment.

FIG. 9 is a time diagram schematically illustrating relations between asystem signal of a neighbouring AN, and a measurement gap.

DETAILED DESCRIPTION

Briefly described, a UE for which an analog beamforming scheme isapplied and a measuring method performed by the UE are provided. Also anAN and a method performed by the AN are provided. Hereinafter, exceptotherwise specified, a UE refers to the one for which an analogbeamforming scheme is applied. A serving AN refers to the one which isproviding services to its served UE. A neighbouring AN refers to the onewhich is working at the same frequency as a served UE currently servicedby a serving AN. A measurement gap refers to a period of time withinwhich a served UE will perform measurement to a neighbouring AN. Asystem signal refers to the one which will be periodically transmittedby a serving AN or a neighbouring AN. It can be, for example, areference signal or a synchronization signal which carries informationabout the serving AN or the neighbouring AN. A transmitting time gaprefers to a period of time during which a system signal is transmitted.In addition, data communication specifically refers to data transmittingor receiving, usually not including control signalling transmitting orreceiving. The term “delay” used herein generally refers to a period oftime taken by the UE to wait for performing measurement after receivinginformation related to measurement time gap from a serving AN. It isdetermined by the serving AN after receiving a measurement request fromthe UE. If there are more than one neighbouring ANs, delayscorresponding to the more than one neighbouring ANs respectively aredetermined by the serving AN and all of their starting times are basedon one time point at which the UE receives information related tomeasurement time gap from the serving AN.

Embodiments of a measuring method 100 performed by a UE for which ananalog beamforming scheme is applied will now be described withreference to FIG. 1.

FIG. 1 illustrates the method 100 comprising transmitting 102, to aserving access node, a measurement request for measuring a neighbouringaccess node which is working at the same frequency as the userequipment; receiving 104, from the serving access node, informationrelated to a series of measurement time gaps; and after a delay,performing 106 measurement to the neighbouring access node within theseries of measurement time gaps.

There are many conditions which can trigger measurement to aneighbouring AN. As an example, if a UE detects a weak signal receivedfrom its serving AN and one aspect of the signal is less than apredetermined threshold for a predefined period of time, the UE willtrigger measurement to a neighbouring AN in order to be serviced by anAN with better signal quality. At this case, the transmitting step 102can be done initiatively by the UE. Herein, the measurement request isspecifically directed to measurement to a neighbouring AN which isworking at the same frequency as the UE, rather than a neighbouring ANwhich is not working at the same frequency as the UE.

The measurement request can play a lot of roles between the UE and itsserving AN herein. As an example, the UE can use the measurement requestto notify the serving AN that measurement will to be performed, so thatthe serving AN can duly suspend data communication with the UE, thusavoiding data lost. As another example, the UE can use the measurementrequest to obtain useful information from its serving AN, such asinformation about a series of measurement time gaps, so that the UE canperform measurement effectively.

After the transmitting step 102, the UE will wait for a response fromthe serving AN. When the serving AN receives the measurement requestfrom the UE, it will determine information related to a series ofmeasurement time gaps and transmit the information to the UE, which willbe discussed in detail hereinafter. When the serving AN transmits theinformation, the UE will perform the receiving step 104, thus obtainingthe information related to the series of measurement time gaps.

When the information related to the series of measurement time gaps isreceived, the performing step 106 can be done by the UE. At this step,the UE will perform measurement within the series of measurement timegaps which are based on the information provided by the serving AN,rather than randomly. In particular, the serving AN can notify theserved UE of exact time when a system signal of a neighbouring AN willbe transmitted. Then, the served UE can use the exact time to performmeasurement. Based on this, time taken by the UE to wait for a systemsignal of a neighbouring AN can be reduced. Therefore, it is highlyeffective in time.

In particular, within each of the series of measurement time gaps, theUE should first suspend data communication with the serving AN, avoidingdata lost during measurement. This is because data from or to theserving AN can not be, in terms of actual effect, received ortransmitted by the UE (in fact, the UE can receive the signals inphysics from a lot of directions. Just because the UE uses the analogbeamforming scheme, the UE can not actually process signalssimultaneously came from such as the serving AN and the neighbouring AN.Therefore, in terms of actual effect, it seems that the UE can notreceive signals simultaneously from a lot of directions, or not transmitsignals in the directions), once the current beamforming pattern of theUE is adjusted (in fact, in this operation, a set of weight valuescorresponding to the current beamforming pattern of the UE are adjusted,so that another beamforming pattern of the UE corresponding to anotherset of weight values is generated. Both of the set of weight values andthe another set of weight values are used for the weighting operationdone by the antenna-array of the UE). Those skilled in the art candesign a lot of methods to do this operation. As an example, the UE canrecord the breakpoint and save information which is helpful forrestoring the data communication later.

Next, the UE will adjust the current (for example, the first)beamforming pattern to a second beamforming pattern in order to receivea system signal of the neighbouring AN. In an embodiment, time taken bythe UE to adjust the beamforming pattern can be considered indetermining the series of measurement time gaps. Details about this willbe discussed later.

Once the adjustment is done, the UE can receive or detect the systemsignal of the neighbouring AN.

After the system signal is received or detected, i.e. after the end ofeach measurement time gap, the UE preferably goes back to the serving ANfrom the detected neighbouring AN. In particular, the UE may re-adjustits beamforming pattern (i.e. re-adjust the second beamforming patternto the first beamforming pattern) to go back to the serving AN. Once theUE is serviced by the serving AN, it may restore the previous datacommunication with the serving AN. Then, the UE will wait for the nextmeasurement time gap to perform measurement. In an embodiment, it may beenough for the UE to measure the system signal of the neighbouring ANonly once. This may occur in a situation in which the signal quality ofthe neighbouring AN is so good that the UE can perform cell switching,for example. At this case, there is no need to measure the system signalof the neighbouring AN again. In another embodiment, measurement may beperformed twice or more by the UE.

In an embodiment, there may be another neighbouring AN which is workingat the same frequency as the UE. At this case, after the receiving step104, the UE also perform measurement to the another neighbouring AN. Inparticular, the UE will perform measurement to the another neighbouringAN within another series of measurement time gaps also provided by theserving AN. In an embodiment, the information about the series ofmeasurement time gaps (which is corresponding to the neighbouring AN)and the another series of measurement gaps (which is corresponding tothe another neighbouring AN) may be provided in the same signal. In analternative embodiment, they can be provided in different signals. Itshould be noted that the another series of measurement time gaps can notoverlap the series of measurement time gaps since the UE uses the analogbeamforming scheme. In particular, if the another series of measurementtime gaps overlap the series of measurement time gaps partly orcompletely, the system signal of one of the neighbouring AN and theanother neighbouring AN can not be detected as described above.Therefore, when receiving the information about measurement time gaps ofthe neighbouring AN and the another neighbouring AN, the UE will performmeasurement to the neighbouring AN and the another neighbouring ANrespectively after different delays. The way in which the delays aredetermined will be discussed hereinafter.

In an embodiment, if there are much more other neighbouring ANs whichare working at the same frequency as the UE, measurement to the moreother neighbouring ANs will be performed according to theabove-described principle.

According to the disclosure, information related to a series ofmeasurement time gaps may comprise length of a delay, a period of theseries of measurement time gaps, and length of each measurement time gapwhich are determined by the serving AN. By means of such information,the UE can know when to perform measurement, thus avoiding time wastewhich results from random measurement. With respect to the information,more details will provided below.

Embodiments herein also relate to a method performed by an AN accordingto an exemplifying embodiment. Such a method will now be described withreference to FIG. 2.

FIG. 2 is a flowchart of a method 200 performed by an AN according to anexemplifying embodiment. FIG. 2 illustrates the method 200 comprisingdetermining 202 information related to a series of measurement time gapsin response to receiving from a served user equipment a measurementrequest for measuring a neighbouring access node which is working at thesame frequency as the user equipment; and transmitting 204 theinformation to the served user equipment.

As shown in FIG. 2, at step 202, after receiving, from a served userequipment, a measurement request for measuring a neighbouring AN whichis working at the same frequency as the user equipment, the AN may knowthat its served UE may need to perform measurement to a neighbouring AN,in order to perform for example cell switching. At this time, the ANwill determine information related to a series of measurement time gapsto cause its served UE perform measurement within the series ofmeasurement time gaps, thus increasing time efficiency and decreasingpower consumption.

In order to determine the series of measurement time gaps, the AN mayneed to know information about a system signal of a neighbouring AN.Therefore, the AN will need to obtain the information about the systemsignal of the neighbouring AN. In an embodiment, after receiving themeasurement request from its served UE, the AN may first communicatewith the neighbouring AN to obtain the system signal of the neighbouringAN, and then determine the information related to a series ofmeasurement time gaps. In another embodiment, the AN may communicatewith the neighbouring AN to obtain the information about the systemsignal of the neighbouring AN and save it in advance. At this case, theAN can use the prestored information to determine the informationrelated to a series of measurement time gaps after receiving themeasurement request.

Now reference will be made to FIG. 9 to schematically explain how todetermine the information related to a series of measurement time gaps.FIG. 9 is a time diagram schematically illustrating relationship betweena system signal of a neighbouring AN and a measurement gap for theneighbouring AN.

In particular, the information related to a series of measurement timegaps may comprise a period of the series of measurement time gaps,length of each measurement time gap and a delay which will be undergoneby the served UE after transmitting a measurement request and beforeperforming measurement. The information related to a series ofmeasurement time gaps may be determined based on system signals of theAN and the neighbouring AN. Since the period of a system signal of theneighbouring AN and the transmitting time gap of the system signal ofthe neighbouring AN could be obtained directly from the neighbouring AN,the most important thing is to determine the delay. Once the delay isdetermined, other information in the information related to the seriesof measurement time gaps can be determined accordingly.

First consider a situation in which one neighbouring AN exists.

In order to determine the information related to the series ofmeasurement time gaps, the serving AN should first know time points atwhich system signals of the neighbouring AN will be transmitted. As anexample, the serving AN can directly obtain an absolute time point atwhich a system signal of the neighbouring AN will be transmitted, aperiod of the system signal of the neighbouring AN and length of thetransmitting time gap of the system signal of the neighbouring AN bycommunicating with the neighbouring AN via a dedicated interface. Inparticular, for example, the serving AN can obtain absolute time pointt2 or absolute time point t6 shown in FIG. 9 from the neighbouring AN.Since the serving AN may also know the period of the system signal ofthe neighbouring AN, it may know all time points at which system signalsof the neighbouring AN will be transmitted. As another example, if theperiod of the system signal of the neighbouring AN is equal to that ofthe system signal of the serving AN, the serving AN can obtain timingdifference between the system signal of the neighbouring AN and thesystem signal of the serving AN along with the period of the systemsignal of the neighbouring AN and length of the transmitting time gap ofthe system signal of the neighbouring AN. The time difference refers torelative time. Assuming that within a certain period, the system signalof the serving AN is transmitted at time point t1 and the system signalof the neighbouring AN is transmitted at time point t2, the timedifference is t2−t1. In such a case, if a time point t3 at which thesystem signal of the serving AN was transmitted is known, a time pointt4 at which the system signal of the neighbouring AN will be transmittedimmediately can also be known based on the above time difference, i.e.t4=t3+(t2−t1).

That is to say, the information related to the series of measurementtime gaps is determined at least based on the system signal of theneighbouring access node, i.e. the serving AN can only use informationabout the system signal of the neighbouring AN to determine theinformation related to the series of measurement time gaps, and theserving AN can also use information about both of system signals of theserving AN and the neighbouring AN to determine it.

However, it should be understood that any other method can be used bythose skilled in the art to obtain the information related to series ofmeasurement time gaps from the above teachings.

Further referring to FIG. 9. As shown in FIG. 9, assuming N_ANrepresents the neighbouring AN; M represents a measurement time gap; theserving AN receives the measurement request at time point t0; and aperiod of time from time points t2 to t4 or time points t6 to t7represents a transmitting time gap of the N_AN within which a systemsignal of the N_AN will be transmitted. However, it should be noted bythose skilled in the art that the time point at which the serving ANreceives the measurement request is used in these embodiments as thestarting time of the delay, only for simplifying description. If timetaken by the serving AN to determine information related to measurementtime gap and time taken by the serving AN to transmit the information tothe served UE are ignored, delays computed by means of the followingmethods are actual delays which will be undergone by the served UE towait for performing measurement. If they are not ignored, those skilledin the art may accordingly adjust the delays computed by the means ofthe following methods to get the actual delays for the served UE.

Return back to FIG. 9 now. The serving AN may know the nearest systemsignal of the neighbouring AN will be transmitted at time point t2according to the above-described method when it receives the measurementrequest. At this case, the delay which will be undergone by the servedUE before performing measurement may be determined as t2−t0.

In addition, in an example as shown in FIG. 9, the period of themeasurement gap can be determined as being equal to that of thetransmitting time gap of the N_AN, for example, a period of time fromtime point t6 to time point t2. In an alternative embodiment, in orderto avoid frequent switching of the UE between the serving AN and theneighbouring AN, the period of the measurement gap can be determined asbeing twice or more times as long as that of the transmitting time gapof the N_AN. That is to say, the period of the measurement time gap canbe a multiple of the period of the system signal of the neighbouringaccess node.

Further, in an example as shown in FIG. 9, length of the measurement gapof the serving AN can be determined as being equal to that of thetransmitting time gap of the N_AN. However, in an alternativeembodiment, time taken by the UE to adjust its beamforming pattern willbe considered. At this case, as shown by the dashed lines in FIG. 9,length of the measurement gap can be determined as being a sum of anoffset and length of the transmitting time gap of the N_AN. As anexample, the offset may be equal to the time taken by the UE to adjustits beamforming pattern. However, many other factors, such as time spenton the transmission path by a system signal, could be considered tocompute the offset.

In such a case, as shown by FIG. 9, the delay may be determined ast1−t0. Use of the offset can guarantee a system signal of theneighbouring AN can be fully received by the served UE without datalost.

Based on the above teachings, many other factors may be considered inmeasurement time gap designs, such as time spent on the transmissionpath, and so on, in order to increase precision of the measurement.

Next, consider a situation in which at least two neighbouring ANs exist.At this case, Since the UE can not detect signals from different ANs interms of actual effect at the same time, the most import thing is that aseries of measurement time gaps corresponding to a neighbouring AN cannot be designed as overlapping another series of measurement time gapscorresponding to another neighbouring AN, which can be done for example,by determining whether the transmitting time gap of a system signal ofthe neighbouring AN overlaps that of a system signal of the anotherneighbouring AN.

If the transmitting time gap of the system signal of the neighbouring ANdoes not overlap that of the system signal of the another neighbouringAN, a delay corresponding to a neighbouring access node can bedetermined as being different from that corresponding to anotherneighbouring access node first, and a period of a series of measurementtime gaps may be determined as being a multiple of a period of thesystem signal of the neighbouring access node and a period of theanother series of measurement time gaps may be determined as being amultiple of a period of the system signal of the another neighbouringaccess node.

Moreover, if the transmitting time gap of the system signal of theneighbouring access node overlaps that of the system signal of theanother neighbouring access node, the delay corresponding to theneighbouring access node can be determined as being different from thatcorresponding to the another neighbouring access node, and a period ofthe series of measurement time gaps may be determined as being at leasttwice as long as a period of the system signal of the neighbouringaccess node, and a period of the another series of measurement time gapsmay be determined as being at least twice as long as a period of thesystem signal of the another neighbouring access node. For example,assuming the transmitting time gaps of the system signal are dividedinto odd number transmitting gaps and even number transmitting gaps. Insuch a case, if a transmitting time gap of a system signal of aneighbouring AN completely or partially overlaps that of a system signalof another neighbouring AN and a period of the system signal of theneighbouring AN is equal to that of the system signal of the anotherneighbouring AN, periods of both of measurement time gaps correspondingto the neighbouring AN and the another neighbouring AN respectively canbe set as being twice as long as the period of the system signal of oneof the neighbouring AN and the another neighbouring AN, and a delaycorresponding to the neighbouring AN can be set to reach an odd numbertransmitting gap and another delay corresponding to the anotherneighbouring AN can be set to reach a even number transmitting gap. Bydoing so, overlapping between the measurement gaps corresponding to theneighbouring AN and the another neighbouring AN respectively may beavoided.

Therefore, overlapping between the series of measurement time gaps andthe another series of measurement time gaps can be overcome for exampleby increasing the period thereof and adjusting the delays.

Return back to FIG. 2 now, after the determining step 202, at step 204,the information related to a measurement time gap may be transmitted tothe served user equipment. Those skilled in the art can design a lot ofways to transmit the information, such as via a broadcast signal or adedicated signal.

In an embodiment, if the serving AN is performing data communicationwith the UE, the method further comprises suspending the datacommunication with the UE after the transmitting step 204. In such acase, the serving AN can use the same method as the UE to suspend thedata communication, which is described above.

Moreover, with respect to the method as shown in FIG. 2, if there isanother neighbouring AN, the method further comprises determininginformation related to another series of measurement time gaps inresponse to receiving from the served user equipment the measurementrequest for measuring another neighbouring access node which is workingat the same frequency as the user equipment. Preferably, the measurementrequest for measuring different neighbouring access nodes is included inthe same message. It is preferred that the information related tomeasurement time gaps for neighbouring access nodes is included in thesame message. For example, the information related to the another seriesof measurement time gaps is included in the information related to theseries of measurement time gaps.

Embodiments herein also relate to a UE for which an analog beamformingscheme is applied according to an exemplifying embodiment. The UE hasthe same objects, technical features as the method performed by the UE.The UE will hence only be described in brief in order to avoidunnecessary repetition.

FIG. 3 is a block diagram of a UE for which an analog beamforming schemeis applied according to an exemplifying embodiment.

FIG. 3 illustrates a UE 300. The UE 300 comprises a processing unit 301adapted to, after the receiving step, after a delay, perform measurementto the neighbouring access node within the series of measurement timegaps; an input unit 303 adapted to receive, from the serving accessnode, information related to a series of measurement time gaps; and anoutput unit 305 adapted to transmit, to a serving access node, ameasurement request for measuring a neighbouring access node which isworking at the same frequency as the user equipment.

Within each of the series of measurement time gaps, the performing stepcomprises: suspending data communication with the serving access node;adjusting a beamforming pattern of the user equipment; and detecting asystem signal of the neighbouring access node.

The processing unit 301 can be further adapted to after the detectingstep, re-adjust the beamforming pattern of the user equipment; andrestore the data communication with the serving access node.

The processing unit 301 can be further adapted to after the receivingstep, after another delay, perform measurement to another neighbouringaccess node within another series of measurement time gaps, wherein theanother neighbouring access node is working at the same frequency as theuser equipment, and information related to the another series ofmeasurement time gaps is included in the information related to theseries of measurement time gaps.

The processing unit 301 may be for example a single processor ormultiple processors. The processing unit 301 may be a single unit or aplurality of units to perform different actions of procedures describedherein. The input unit 303 and the output unit 305 may be arranged as anintegrated entity (for example, an antenna) or separate entities (forexample, a transmitter or a receiver).

Furthermore, the UE 300 may comprise a memory 307 for storinginformation. The memory 307 may be a volatile or non-volatile memory,e.g. an EEPROM (Electrically Erasable Programmable Read-Only Memory), aflash memory and/or a hard drive, and so on.

The UE 300 may have the same advantages as the method performed by theUE 300.

Embodiments herein also relate to an AN according to an exemplifyingembodiment. The AN has the same objects, technical features as themethod performed by the AN. The AN will hence only be described in briefin order to avoid unnecessary repetition.

FIG. 4 is a block diagram of an AN according to an exemplifyingembodiment.

FIG. 4 illustrates an AN 400. The UE 400 comprises a processing unit 401adapted to determine information related to a series of measurement timegaps in response to receiving from a served user equipment a measurementrequest for measuring a neighbouring access node which is working at thesame frequency as the user equipment; an input unit 403 adapted toreceiving the measurement request from the served user equipment; and anoutput unit 405 adapted to transmit the information to the served userequipment.

In addition, the processing unit 401 can be further adapted to after thetransmitting step, suspend data communication with the served userequipment.

In addition, the processing unit 401 can be further adapted to beforethe determining step, obtain the system signal of the neighbouringaccess node from the neighbouring access node, wherein the informationrelated to the series of measurement time gaps is at least determinedbased on the system signal of the neighbouring access node.

In addition, the processing unit 401 can be further adapted to determineinformation related to another series of measurement time gaps inresponse to receiving from the served user equipment a measurementrequest for measuring another neighbouring access node which is workingat the same frequency as the user equipment. The output unit 405 can befurther adapted to transmit, to the served user equipment, theinformation related to the another series of measurement time gaps.

In an embodiment, the information related to the series of measurementtime gaps comprises a delay, a period of the series of measurement timegaps, and length of each measurement time gap.

The processing unit 401 may be for example a single processor ormultiple processors. The processing unit 401 may be a single unit or aplurality of units to perform different actions of procedures describedherein. The input unit 403 and the output unit 405 may be arranged as anintegrated entity (for example, an antenna) or separate entities (forexample, a transmitter or a receiver).

Furthermore, the AN 400 may comprise a memory 407 for storinginformation. The memory 407 may be a volatile or non-volatile memory,e.g. an EEPROM (Electrically Erasable Programmable Read-Only Memory), aflash memory and/or a hard drive, and so on.

The AN may have the same advantages as the method performed by the AN.

Embodiments herein also relate to a UE for which an analog beamformingscheme is applied according to an exemplifying embodiment. The UE hasthe same objects, technical features as the method performed by the UE.The UE will hence only be described in brief in order to avoidunnecessary repetition.

FIG. 5 is a block diagram of a UE for which an analog beamforming schemeis applied according to an exemplifying embodiment.

FIG. 5 illustrates a UE 500 comprises a processor 501 and memory 503.The memory comprises instructions which when executed by the processor501 causes the UE 500 to transmit, to a serving access node, ameasurement request for measuring a neighbouring access node which isworking at the same frequency as the user equipment; receive, from theserving access node, information related to a series of measurement timegaps; and after the receiving step, after a delay, perform measurementto the neighbouring access node within the series of measurement timegaps.

Within each of the series of measurement time gaps, the performing stepcomprises: suspending data communication with the serving access node;adjusting a beamforming pattern of the user equipment; and detecting asystem signal of the neighbouring access node.

In an embodiment, the memory (503) further comprises instructions, whichwhen executed by the processor (501) causes the user equipment (500) to:after the detecting step, re-adjust the beamforming pattern of the userequipment; and restore the data communication with the serving accessnode.

In an embodiment, the memory (503) further comprises instructions, whichwhen executed by the processor (501) causes the user equipment (500) to:after the receiving step, after another delay, perform measurement toanother neighbouring access node within another series of measurementtime gaps, wherein the another neighbouring access node is working atthe same frequency as the user equipment, and information related to theanother series of measurement time gaps is included in the informationrelated to the series of measurement time gaps.

The UE may have the same advantages as the method performed by the UE.

Embodiments herein also relate to an AN according to an exemplifyingembodiment. The AN has the same objects, technical features as themethod performed by the AN. The AN will hence only be described in briefin order to avoid unnecessary repetition.

FIG. 6 is a block diagram of an AN according to an exemplifyingembodiment.

FIG. 6 illustrates the AN 600 comprising a processor 601 and memory 603.the memory 603 comprising instructions which when executed by theprocessor 601 causes the access node 600 to: determine informationrelated to a series of measurement time gaps in response to receivingfrom a served user equipment a measurement request for measuring aneighbouring access node which is working at the same frequency as theuser equipment; and transmit the information to the served userequipment.

In an embodiment, the memory 603 further comprises instructions, whichwhen executed by the processor 601 causes the access node 600 to: afterthe transmitting step, suspend data communication with the served userequipment.

In an embodiment, the memory 603 further comprises instructions, whichwhen executed by the processor 601 causes the access node 600 to: beforethe determining step, obtain the system signal of the neighbouringaccess node from the neighbouring access node, wherein the informationis determined at least based on the system signal of the neighbouringaccess node.

In an embodiment, the information the series of measurement time gapscomprises a delay, a period of the series of measurement time gaps,length of each measurement time gap.

In an embodiment, the memory 603 further comprises instructions, whichwhen executed by the processor 601 causes the access node 600 to:determine information related to another series of measurement time gapsin response to receiving from the served user equipment a measurementrequest for measuring another neighbouring access node which is workingat the same frequency as the user equipment; and transmit, to the serveduser equipment, the information related to the another series ofmeasurement time gaps.

The AN may have the same advantages as the method performed by the AN.

Embodiments herein also relate to a UE for which an analog beamformingscheme is applied according to an exemplifying embodiment. The UE hasthe same objects, technical features as the method performed by the UE.The UE will hence only be described in brief in order to avoidunnecessary repetition.

FIG. 7 is a block diagram of a UE for which an analog beamforming schemeis applied according to an exemplifying embodiment.

FIG. 7 illustrates the UE 700 comprising a transmitting unit 701 fortransmitting, to a serving access node, a measurement request formeasuring a neighbouring access node which is working at the samefrequency as the user equipment; a receiving unit 703 for receiving,from the serving access node, information related to a series ofmeasurement time gaps; and a performing unit 705 for after the receivingstep, after a delay, performing measurement to the neighbouring accessnode within the series of measurement time gaps.

In an embodiment, within each of the series of measurement time gaps,the performing step comprises: suspending data communication with theserving access node; adjusting a beamforming pattern of the userequipment; and detecting a system signal of the neighbouring accessnode.

In an embodiment, the UE further comprises a re-adjusting unit 707 forre-adjusting the beamforming pattern of the user equipment; and arestoring unit 709 for restoring the data communication with the servingaccess node.

In an embodiment, the UE further comprises another performing unit 711for after the receiving step, after another delay, performingmeasurement to another neighbouring access node within another series ofmeasurement time gaps, wherein the another neighbouring access node isworking at the same frequency as the user equipment, and informationrelated to the another series of measurement time gaps is included inthe information related to the series of measurement time gaps.

The UE may have the same advantages as the method performed by the UE.

It should be noted that FIG. 7 merely illustrates various functionalunits in the UE 700 in a logical sense. The functions in practice may beimplemented using any suitable software and hardware means/circuits etc.Thus, the embodiments are generally not limited to the shown structuresof the UE 700 and the functional units.

Embodiments herein also relate to an AN according to an exemplifyingembodiment. The AN has the same objects, technical features as themethod performed by the AN. The AN will hence only be described in briefin order to avoid unnecessary repetition.

FIG. 8 is a block diagram of an AN according to an exemplifyingembodiment.

FIG. 8 illustrates the AN 800 comprising a determining unit 801 fordetermining information related to a series of measurement time gaps inresponse to receiving from a served user equipment a measurement requestfor measuring a neighbouring access node which is working at the samefrequency as the user equipment; and a transmitting unit 803 fortransmitting the information to the served user equipment.

In an embodiment, the AN further comprises a suspending unit 805 forafter the transmitting step, suspending data communication with theserved user equipment.

In an embodiment, the AN further comprises an obtaining unit 807 forbefore the determining step, obtaining the system signal of theneighbouring access node from the neighbouring access node, wherein theinformation is determined at least based on the system signal of theneighbouring access node.

In an embodiment, the information related to the series of measurementtime gaps comprises a delay, a period of the series of measurement timegaps, length of each measurement time gap.

In an embodiment, the AN further comprises another determining unit 809for determining information related to another series of measurementtime gaps in response to receiving from the served user equipment themeasurement request for measuring another neighbouring access node whichis working at the same frequency as the user equipment, and theinformation related to the another series of measurement time gaps isincluded in the information related to the series of measurement timegaps.

The AN may have the same advantages as the method performed by the AN.

Furthermore, it should be noted that FIG. 8 merely illustrates variousfunctional units in the AN 800 in a logical sense. The functions inpractice may be implemented using any suitable software and hardwaremeans/circuits etc. Thus, the embodiments are generally not limited tothe shown structures of the AN 800 and the functional units.

In an embodiment, a UE according to the disclosure may comprise acomputer program comprising instructions which, when executed on atleast one processor, cause the at least one processor to carry out theabove method performed by the UE; and a carrier comprising the computerprogram.

In an embodiment, an AN according to the disclosure may comprise acomputer program comprising instructions which, when executed on atleast one processor, cause the at least one processor to carry out theabove method performed by the AN; and a carrier comprising the computerprogram.

It is to be understood that the choice of interacting units, as well asthe naming of the units within this disclosure are only for exemplifyingpurpose, and nodes suitable to execute any of the methods describedabove may be configured in a plurality of alternative ways in order tobe able to execute the suggested procedure actions.

It should also be noted that the units described in this disclosure areto be regarded as logical entities and not with necessity as separatephysical entities.

While the embodiments have been described in terms of severalembodiments, it is contemplated that alternatives, modifications,permutations and equivalents thereof will become apparent upon readingof the specifications and study of the drawings. It is thereforeintended that the following appended claims include such alternatives,modifications, permutations and equivalents as fall within the scope ofthe embodiments and defined by the pending claims.

1. A measuring method performed by a user equipment for which an analogbeamforming scheme is applied, the method comprising: transmitting, to aserving access node, a measurement request for measuring a neighbouringaccess node that is working at a same frequency as the user equipment;receiving, from the serving access node, information related to a seriesof measurement time gaps; and after a delay, performing a measurement tothe neighbouring access node within the series of measurement time gaps.2. The measuring method according to claim 1, wherein within each of theseries of measurement time gaps, the performing comprises: suspendingdata communication with the serving access node; adjusting a beamformingpattern of the user equipment; and detecting a system signal of theneighbouring access node.
 3. The measuring method according to claim 2,further comprising: after the detecting, re-adjusting the beamformingpattern of the user equipment; and restoring the data communication withthe serving access node.
 4. The measuring method according to claim 1,wherein the information comprises a length of the delay, a period of theseries of measurement time gaps, and a length of each measurement timegap.
 5. The measuring method according to claim 4, wherein the period ofthe series of measurement time gaps is a multiple of a period of asystem signal of the neighbouring access node, and the length of eachmeasurement time gap is equal to a sum of an offset and a length of atransmitting time gap within which the system signal of the neighbouringaccess node is transmitted.
 6. The measuring method according to claim1, further comprising: after another delay, performing measurement toanother neighbouring access node within another series of measurementtime gaps, wherein the another neighbouring access node is working atthe same frequency as the user equipment, and information related to theanother series of measurement time gaps is included in the informationrelated to the series of measurement time gaps.
 7. The measuring methodaccording to claim 6, wherein the delay is different from the anotherdelay and the series of measurement time gaps do not overlap the anotherseries of measurement time gaps.
 8. A method performed by an accessnode, the method comprising: determining information related to a seriesof measurement time gaps in response to receiving from a served userequipment a measurement request for measuring a neighbouring access nodethat is working at a same frequency as the user equipment; andtransmitting the information to the served user equipment.
 9. The methodaccording to claim 8, further comprising: after the transmitting,suspending data communication with the served user equipment.
 10. Themethod according to claim 8, wherein the information related to theseries of measurement time gaps is determined at least based on a systemsignal of the neighbouring access node.
 11. The method according toclaim 8, wherein the information comprises: a delay, a period of theseries of measurement time gaps, and a length of each measurement timegap.
 12. The method according to claim 8, further comprising:determining information related to another series of measurement timegaps in response to receiving from the served user equipment ameasurement request for measuring another neighbouring access node thatis working at the same frequency as the user equipment, and theinformation related to the another series of measurement time gaps isincluded in the information related to the series of measurement timegaps.
 13. The method according to claim 12, wherein the series ofmeasurement time gaps do not overlap the another series of measurementtime gaps.
 14. The method according to claim 13, wherein if atransmitting time gap of a system signal of the neighbouring access nodedoes not overlap that of a system signal of the another neighbouringaccess node, a delay corresponding to the neighbouring access node isdifferent from that corresponding to the another neighbouring accessnode, and a period of the series of measurement time gaps is a multipleof a period of the system signal of the neighbouring access node, and aperiod of the another series of measurement time gaps is a multiple of aperiod of the system signal of the another neighbouring access node. 15.The method according to claim 13, wherein if a transmitting time gap ofa system signal of the neighbouring access node overlaps that of asystem signal of the another neighbouring access node, a delaycorresponding to the neighbouring access node is different from thatcorresponding to the another neighbouring access node, and a period ofthe series of measurement time gaps is at least twice as long as aperiod of the system signal of the neighbouring access node, and aperiod of the another series of measurement time gaps is at least twiceas long as a period of the system signal of the another neighbouringaccess node. 16-24. (canceled)
 25. A user equipment for which an analogbeamforming scheme is applied, the user equipment comprising: aprocessor and a memory, the memory including instructions which whenexecuted by the processor cause the user equipment to: transmit, to aserving access node, a measurement request for measuring a neighbouringaccess node that is working at a same frequency as the user equipment;receive, from the serving access node, information related to a seriesof measurement time gaps; and after a delay, perform a measurement tothe neighbouring access node within the series of measurement time gaps.26. The user equipment according to claim 25, wherein within each of theseries of measurement time gaps, to perform the measurement includes: tosuspend data communication with the serving access node; to adjust abeamforming pattern of the user equipment; and to detect a system signalof the neighbouring access node.
 27. The user equipment according toclaim 26, wherein the memory includes further instructions, which whenexecuted by the processor cause the user equipment to: re-adjust thebeamforming pattern of the user equipment; and restore the datacommunication with the serving access node.
 28. An access nodecomprising: a processor and a memory, the memory including instructionswhich when executed by the processor cause the access node to: determineinformation related to a series of measurement time gaps in response toreceiving from a served user equipment a measurement request formeasuring a neighbouring access node that is working at a same frequencyas the user equipment; and transmit the information to the served userequipment.
 29. The access node according to claim 28, wherein the memoryincludes further instructions, which when executed by the processorcause the access node to: after the transmitting, suspend datacommunication with the served user equipment.
 30. The access nodeaccording to claim 28, wherein the information includes a delay, aperiod of the series of measurement time gaps, and a length of eachmeasurement time gap.
 31. A user equipment for which an analogbeamforming scheme is applied, the user equipment comprising: atransmitting unit to transmit, to a serving access node, a measurementrequest for measuring a neighbouring access node that is working at asame frequency as the user equipment; a receiving unit to receive, fromthe serving access node, information related to a series of measurementtime gaps; and a performing unit to perform, after a delay, ameasurement to the neighbouring access node within the series ofmeasurement time gaps.
 32. An access node comprising: a determining unitto determine information related to a series of measurement time gaps inresponse to receiving from a served user equipment a measurement requestfor measuring a neighbouring access node that is working at a samefrequency as the user equipment; and a transmitting unit to transmit theinformation to the served user equipment.
 33. (canceled)
 34. The userequipment according to claim 25, wherein the memory includes furtherinstructions, which when executed by the processor cause the userequipment to: after another delay, perform a measurement to anotherneighbouring access node within another series of measurement time gaps,wherein the another neighbouring access node is working at the samefrequency as the user equipment, and information related to the anotherseries of measurement time gaps is included in the information relatedto the series of measurement time gaps.
 35. The access node according toclaim 28, wherein the memory includes further instructions, which whenexecuted by the processor cause the access node to: determine theinformation at least based on a system signal of the neighbouring accessnode.
 36. The access node according to claim 28, wherein the memoryincludes further instructions, which when executed by the processorcause the access node to: determine information related to anotherseries of measurement time gaps in response to receiving from the serveduser equipment a measurement request for measuring another neighbouringaccess node that is working at the same frequency as the user equipment;and transmit, to the served user equipment, the information related tothe another series of measurement time gaps.